In a conventional art, as a rotor structure of a permanent magnetic type rotary machine such as a permanent magnetic type super high speed synchronous motor and permanent magnetic type synchronous motor, it has been well known various rotor structures. For example, a permanent magnet formed cylindrically is fitted to a non-magnetic high reinforcement material (hereinafter, it is referred as “reinforce ring”) by a press-in method, a shrinkage fitting method or a cooling fitting method and a permanent magnet formed cylindrically is wound by a non-magnetic metal wire (see Patent Documents 1 and 2.
In a rotor structure with a ring magnet as described above, an interference is acting on the reinforce ring as described above so as to prevent a permanent magnet from being damaged caused by tensile stress acting on an inner diameter of the permanent, magnet while the rotor structure is rotated at high speed, wherein a level of occurred tensile stress is higher than an acceptable tensile stress level of the permanent magnet. Further, concerning with rotational torque acting on a permanent magnet, the interference is provided so as not to separate the permanent magnet from a rotor shaft while the rotor structure is rotated at high speed. Alternatively, the rotor shaft and the permanent magnet are bonded so as to transmit the rotational torque to the rotor shaft. In order to reduce eddy current loss, high strength fiber such as carbon fiber and/or a non-magnetic metal wire are utilized as a reinforce ring.
On the other hand, there is another rotor structure wherein a column-shaped permanent magnet is attached to a reinforce ring by the press-in method, the shrinkage fitting method or the cooling fitting method (see Patent Document 3).
In the case of the rotor structure with the column-shaped permanent magnet, an interference is provided so as not to apply tensile stress of which a strength is not higher than a level of an acceptable tensile stress of the permanent magnet on the permanent magnet in the case that the rotor structure is rotated at high speed in order to prevent the permanent magnet from being broken. The reinforce ring and the rotor shaft are attached at the both ends of the permanent magnet by the press-in method, a cooling fitting method or a welding method. Rotational torque acting on the permanent magnet is transmitted to the rotor shaft through the interference. The interference affects the reinforce ring and the permanent magnet are not separated and the rotor shaft and the permanent magnet are not separated even if centrifugal force is occurred by rotating the rotor structure at high speed. Upon comparing a collar-shaped permanent magnet and a permanent magnet formed cylindrically in the condition that the both magnets have the same diameter and the same length, the column-shaped permanent magnet is not baneful influenced by centrifugal force and magnetomotive force produced by the column-shaped permanent magnet is stronger than that produced by the permanent magnet formed cylindrically.